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<p>Heterotrophic diazotrophic bacteria (HDB) are increasingly recognized as widespread and significant contributors to oceanic nitrogen fixation. Macroalgae are known to form stable associations with endophytic and epiphytic bacteria for their growth, development and defense. The red alga <i>Kappaphycus alvarezii</i> can grow under nutrient-limited conditions, suggesting that nutritionally beneficial microbial associations may help sustain its growth under these conditions. The present study investigated the presence of HDB associated with <i>K. alvarezii</i> by incubating surface sterilized thallus sections in nitrogen-limited media. The isolates were taxonomically identified using 16S rRNA gene analysis, and their diazotrophic potential was assessed by amplifying the <i>nifH</i> gene. Phylogenetic analysis revealed associations with diverse genera, including <i>Yangia, Salipiger, Mangrovicoccus, Tritonibacter, Pseudooceanicola, Roseibium</i>, <i>Thalassospira</i>, <i>Oceanobacillus</i>, <i>Alteromonas, Marinobacter, Pseudomonas</i>, <i>Stutzerimonas</i> and <i>Tenacibaculum.</i> Eleven percent of the isolates, including <i>Salipiger</i> sp., <i>Yangia</i> sp., <i>Thalassospira</i> sp. <i>Mangrovicoccus ximenensis</i> and <i>Stutzerimonas stutzeri</i> tested positive for the presence of <i>nifH</i> gene, indicating potential diazotrophic capability. Our findings indicate that <i>K. alvarezii</i> hosts a diverse assemblage of culturable bacteria with potential host-beneficial functions, highlighting the need for functional validation of their contributions to the nitrogen acquisition and fitness of <i>K. alvarezii</i>. </p> Graphical abstract

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Diversity and diazotrophic potential of culturable bacteria associated with the red seaweed Kappaphycus alvarezii

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月15日

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  • Sweeta Peter Emerson,
  • Seena Jose,
  • Aparna Prasamsa Golla,
  • Akash Kumar,
  • Sri Sailaja Nori,
  • Shrikumar Suryanarayanan,
  • I. S. Bright Singh,
  • Valsamma Joseph

摘要

Heterotrophic diazotrophic bacteria (HDB) are increasingly recognized as widespread and significant contributors to oceanic nitrogen fixation. Macroalgae are known to form stable associations with endophytic and epiphytic bacteria for their growth, development and defense. The red alga Kappaphycus alvarezii can grow under nutrient-limited conditions, suggesting that nutritionally beneficial microbial associations may help sustain its growth under these conditions. The present study investigated the presence of HDB associated with K. alvarezii by incubating surface sterilized thallus sections in nitrogen-limited media. The isolates were taxonomically identified using 16S rRNA gene analysis, and their diazotrophic potential was assessed by amplifying the nifH gene. Phylogenetic analysis revealed associations with diverse genera, including Yangia, Salipiger, Mangrovicoccus, Tritonibacter, Pseudooceanicola, Roseibium, Thalassospira, Oceanobacillus, Alteromonas, Marinobacter, Pseudomonas, Stutzerimonas and Tenacibaculum. Eleven percent of the isolates, including Salipiger sp., Yangia sp., Thalassospira sp. Mangrovicoccus ximenensis and Stutzerimonas stutzeri tested positive for the presence of nifH gene, indicating potential diazotrophic capability. Our findings indicate that K. alvarezii hosts a diverse assemblage of culturable bacteria with potential host-beneficial functions, highlighting the need for functional validation of their contributions to the nitrogen acquisition and fitness of K. alvarezii.

Graphical abstract